Bone anchoring device

ABSTRACT

A bone anchoring device includes a receiving part for receiving a rod, the receiving part having a first bore coaxial with a longitudinal axis and a second bore. The bone anchoring device also includes an anchoring element having a first end for insertion into the bone and a second end positionable within a second bore, the second end having a spherically shaped surface portion. The bone anchoring device further has a locking device provided to the second bore of the receiving part. The locking device protrudes from an inner wall of the second bore and engages with a recessed surface portion of the second end of the anchoring element, such that the anchoring element is pivotable relative to the receiving part around a single axis of rotation. The locking device may comprise pins inserted into through holes formed in the receiving part, which engage with the recessed surface portion of the second end.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.11/934,625, filed Nov. 2, 2007, now U.S. Pat. No. 7,892,259 which claimspriority to and the benefit of U.S. Provisional Patent Application No.60/859,642, filed Nov. 17, 2006, and claims priority from EuropeanPatent Application EP 06023910.0, filed Nov. 17, 2006, the disclosuresof which are incorporated herein by reference.

BACKGROUND

The invention relates to a bone anchoring device which comprises areceiving part for receiving a rod, an anchoring element having a firstend for insertion into the bone and a second end held in the receivingpart, and a locking device to limit a pivoting movement of the anchoringelement to pivoting around a single axis.

Document US 2006/0155277 A1 discloses an anchoring element, whichcomprises a retaining means for receiving a rod, the retaining meanshaving a ring-shaped mount, a fastening element for anchoring the devicein the vertebra, and a securing element which can be screwed into athread of the retaining means in order to fix the fastening element withan angle relative to the retaining means.

The fastening element comprises a threaded shank and a bearing, thelatter being provided to achieve a pivotal motion when being supportedby a separate intermediate element, which can be inserted into thering-shaped mount of the retaining means. More specifically, the bearingincludes spherical surfaces which engage with spherical counterparts ofthe intermediate element. The bearing further has two flat guidingsurfaces formed on opposite sides thereof, which engage withrespectively flat counter surfaces of the intermediate element.

The fastening element may perform a rotation movement around one singleaxis with respect to the intermediate element. However, the intermediateelement can freely rotate within the mount around a longitudinal axis ofthe retaining means. Hence, a polyaxial adjustment of the fasteningelement relative to the retaining means is possible.

The final fixation is achieved by screwing the securing element into thethread of the retaining means after the rod is inserted. As a resultthereof, pressure is exerted onto the rod, which transmits this pressurefurther to the intermediate element which then frictionally clamps thebearing. Thus, upon fixation by the securing element, the degree of freemovement is reduced from polyaxial to fully rigid at the same time.

For certain applications it is desirable to have a bone anchoring devicewhich allows an adjustment of the angle between the bone anchoringelement and the receiving part in one single plane.

Based on the foregoing, there is a need for a bone anchoring device,which simplifies handling of an anchoring device and increases itsstability against external forces once the device has been fixated usinga fixation element.

SUMMARY

The present bone anchoring device is arranged to reduce rotation of theanchoring element to rotation around one single axis prior to fixation.For this purpose, a locking device is provided at an inner wall of thereceiving part which engages with the surface of the head of theanchoring element in order to impede rotation of the anchoring elementaround, e.g., a longitudinal axis of the receiving part. The lockingdevice and the engaging surface are constructed such as to allow pivotalmotion around one single axis, which in this example may be orientedperpendicular to the longitudinal axis.

As a result, there is only one axis of rotation upon installation of theanchoring devices and the rod. The handling during installation may thusbe simplified. Limiting the pivotal movement of the anchoring deviceswith regard to the receiving part to just one single axis serves tosimplify the handling of the parts of the anchoring device duringapplication to the bones and increases the stability of the installedparts with respect to external forces.

Further features and advantages of the bone anchoring device will becomeapparent and will be best understood by reference of the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective exploded view of a bone anchoring deviceaccording to an embodiment prior to assembly;

FIG. 2 shows a perspective exploded view of the bone anchoring deviceaccording to

FIG. 1, but after partial assembly;

FIG. 3 shows a partial sectional view of the bone anchoring deviceaccording to the partially assembled state of FIG. 2, with a sectionalplane defined by a longitudinal axis and a pivotal axis;

FIG. 4 shows a perspective view of an anchoring element;

FIG. 5 shows a top view of a head of the anchoring element shown in FIG.4;

FIG. 6 a shows a side view of the anchoring element shown in FIG. 4 withflat guiding surface portions seen in profile;

FIG. 6 b shows a side view of the anchoring element shown in FIG. 6 a,but with flat guiding surface portions oriented towards observer (90degrees rotated);

FIGS. 7 a-c show an alternative embodiment of a head with flat guidingsurfaces being inclined with respect to an axis of the shank of theanchoring element;

FIG. 8 shows the arrangement of through holes in a cross-sectionalprofile through a horizontal plane labeled as 42 in FIG. 3, the planecontaining the rotational axis;

FIG. 9 shows an alternative embodiment of an arrangement of throughholes;

FIGS. 10 a, b show alternative embodiments of pins;

FIGS. 11 a, b show an embodiment wherein the through holes are arrangedin a longitudinal direction with respect to the receiving part;

FIGS. 12 a, b show an embodiment wherein only one through hole is formedin the receiving part, with FIG. 12 a showing an exploded view, whereasFIG. 12 b shows a cross-sectional profile in a horizontal plane withrespect to the receiving part.

DETAILED DESCRIPTION

FIGS. 1 to 3 show in a perspective view a first embodiment of a boneanchoring device, wherein FIG. 1 reveals a situation prior to assembly,FIG. 2 shows details after assembly, and FIG. 3 shows a partly crosssectional profile of the embodiment illustrated in FIGS. 1 and 2 withoutrod and fixation element.

The bone anchoring device includes a receiving part 1 which has a firstend 2 and a second end 3 opposite to the first end. The two ends extendperpendicular to a longitudinal axis 4. Coaxially formed with thelongitudinal axis 4, a bore 5 is provided which extends from the firstend 2 to a predetermined distance from the second end 3. At the secondend 3 an opening or second bore 6 is provided, the diameter of which issmaller than the diameter of the bore 5. The coaxial bore 5 taperstowards the opening 6 in a section 7 which can be for examplespherically, conically or otherwise shaped.

The receiving part 1 further has a substantially U-shaped recess 8 whichstarts from the first end 2 and extends in the direction of the secondend 3 to a predetermined distance from said second end 3. By means ofthe U-shaped recess 8 two free legs 9, 10 are formed extending towardsthe first end 2.

Adjacent to the first end 2, the receiving part 1 includes an internalthread 11 on said legs 9, 10. The U-shaped recess 8 serves for receivinga rod 12 by which several bone anchoring devices can be connected. Ascrew 30 cooperating with the internal thread is used as a fixationelement. The U-shaped recess 8 further defines an axis 31 along whichthe rod 12 is oriented upon installation in the U-shaped recess 8. Inthis specific embodiment, axis 31 is perpendicular to the longitudinalaxis 4.

The bone anchoring device further has a bone anchoring element 13 whichincludes a shank 14 with a bone thread and a head 15 at one end. It isnoted that the shank 14 of the anchoring element 13 may not necessarilybe threaded and may include other forms suited to apply the anchoringdevice.

As shown in more detail in FIGS. 4 to 6, the head 15 has a sphericalsurface portion 16 with the center M (not shown) of a respective sphere36 lying in the center of the head 15. The head 15 further has twosubstantially flat surface portions 35 a, 35 b recessed from an idealsphere as defined by spherical surface portion 16. The flat surfaceportions are positioned on opposite sides of the head 15 and areoriented parallel to each other.

On the side opposite to the shank 14, the head 15 may include a flatsurface 18. A recess 19 for engagement with a screwing-in tool can beprovided in the flat surface 18. The head 15 rests in the section 7 ofthe receiving part 1 which thus forms a seat for the head 15.

A pressure element 20 is provided for acting onto the head 15. Thepressure element 20 is substantially cylindrically-shaped and comprisesa first end 21 and a second end 22. The outer diameter of the pressureelement 20 is slightly smaller than the inner diameter of the bore 5 ofthe receiving part 1 so that the pressure element 20 can be insertedinto the receiving part 1 and can slide within the bore 5. Adjacent tothe first end 21 the pressure element 20 comprises a cylindricalsegment-shaped recess 23, the size of which is such that the rod 12 fitsin the recess 23.

Adjacent to the second end 22 the pressure element 20 includes aspherically shaped inner surface. The radius of the sphere correspondsto that of the head 15. The pressure element 20 further has a coaxialbore 28 for allowing access for a screwing in tool to the recess 19 inthe head 15. The pressure element 20 can further be secured againstfalling out of the receiving part 1 once it has been inserted, oragainst rotation within the receiving part 1, for example by means ofcrimp bores 27 or means exerting a similar function. However, the boneanchoring device is not limited thereto.

The receiving part 1 according to this embodiment further includes twothrough holes 34 each receiving a pin 33. The diameter of the pins 33corresponds to that of the through holes 34. The through holes 34 arelocated on opposite sides in the region of the seat 7 and traverse thebody of receiving part 1. The through holes 34 also traverse an innerspace as defined by the seat 7 of the receiving part 1, which becomesvisible from a cross-sectional profile of a plane perpendicular to thelongitudinal axis 4 as shown in FIG. 8. More specifically, the throughholes 34 are open towards the inner wall of the seat 7 of the receivingpart 1. Consequently, the diameter of the space defined by the seat 7 isreduced, when pins 33 are inserted into the through holes 34. In otherwords the pins 33 protrude from the inner surface of the seat 7 whenresiding within the through holes 34.

Once being inserted into the through holes 34 of the body of thereceiving part 1, the pins 33 engage with the flat surface portions 35a, 35 b of the head 15 of the anchoring element 13. As a result thereof,the head 15 cannot be rotated within a plane perpendicular to thelongitudinal axis 4 due to the presence of the pins 33, as it isillustrated in FIG. 8. However, as the flat surfaces 35 a, 35 b serve asguiding surfaces, a pivotal motion around a rotation axis 46 as shown inFIG. 2 is retained.

In this embodiment, the U-shaped recess 8 is aligned with the directionof the through holes 34, such that the rotation axis 46 is perpendicularto the longitudinal axis 4 and to the rod axis 31. Accordingly, rotationof the anchoring element 13 is enabled in a plane defined by thelongitudinal axis 4 and the axis 31 (see FIG. 2). It is noted, however,that it is also within the scope of the invention to orient the throughholes (and thus the pins upon insertion) perpendicular to the rod axis.Rotation is then enabled in a plane perpendicular to the rod direction.

It becomes clear to the person skilled in the art, that any direction ofthe through holes 34 as formed in the receiving part 1 may beconstructed according the specific needs. FIG. 9 shows anotherembodiment, wherein multiple through holes 34 a, 34 b are formedperpendicular to and cross each other. The pin may be inserted eitherinto through hole 34 a, or alternatively into through hole 34 b. Onlyone through hole 34 a, 34 b per direction is shown. Using the boneanchoring device according to this embodiment, the surgeon may in-situdecide which rotational axis is presently preferred to achievestability.

According to a further embodiment illustrated in FIGS. 7 a-c, theorientation of the surface normal 41 of the flat guiding surfaces 35 c,35 d is inclined with respect to a plane defined by the top surface 18of the anchoring element 13. As a result inclined angles a of thethreaded shafts 14 with respect to the longitudinal axis 4 of thereceiving part 1 may be accomplished. A set of anchoring elements withdifferent inclination angles α=0°, 5°, 10°, 15°, etc., respectively, maybe supplied for example, from which the surgeon may choose according tothe situation. It is noted that the rotation axis 46 is retained in thisembodiment.

It is noted that the whole device including the pins is preferably madeof a biocompatible material, for example titanium, titanium alloy orstainless steel, etc.

The bone anchoring device described in the present embodiments may beassembled upon the instance of actually carrying out surgery. However,the device may as well be preassembled. In such a preassembledcondition, the anchoring element is screwed into the bone.

In the specific embodiments detailed herein pivoting within a singleplane is accomplished by means of the pins 33 acting onto the flatguiding surfaces 35 a-d of head 15, which allows pivoting aroundrotation axis 46, but prevents pivoting around other axes 4, 31.Therefore, an adjustment of the position of the receiving part 1 withrespect to the anchoring element 13 within a plane that includes the rodaxis is possible, whereas an adjustment in a direction perpendicular tothe rod axis is blocked according to the present embodiments.

After adjustment of the position of the receiving part 1 the rod 12 isinserted and the inner screw 30 is screwed-in between the legs 9, 10 andtightened to exert a pressure onto the rod 12. The rod 12 transmits thepressure to the pressure element, which itself exerts a pressure ontothe head 15 to lock it in its final position.

FIGS. 10 a and 10 b show an outline of alternative embodiments for thepins 33. In the previous embodiments, the pins 33 a are shown to have acircular cross-section. The embodiment of FIG. 10 a, however,illustrates that the same effect may be achieved using pins 33 b havinga semi-circular cross-section. As shown in FIG. 10 b, a square orrectangular profiled pin 33 c, 33 e or an elliptical pin 33 f, etc. arealso possible. Preferred are cylindrical pins for the reason of easiermanufacturing. However, flat shapes are also advantageous as theseprovide a particularly tight contact to the flat surfaces 35 a, 35 b.

With regard to a semi-circular pin 33 d further illustrated in thebottom section of FIG. 10 b, the respective through hole may be arrangedsuch that the pins 33 d only protrude from the inner surface of the bore6 or tapered section 7, if the pin 33 d is rotated within the bore ofthe through hole 34. A fixing means (not shown) may be actuated suchthat this position of the pin 33 d within the through hole 34 isretained. An advantage arises as upon spinal surgery the pins mayalready be inserted prior to applying the anchoring element 13 to thebone. The surgeon merely has to actuate the pin 33 d by rotating itwithin the through hole 34, when a reduction of pivoting movement isdesired.

In an alternate embodiment, the fixation element 30 may be composed ofan inner member and an outer member (not shown). The outer member isthreaded for screwing it into internal thread 11 of the receiving part.A bottom surface of the outer member of the fixation element 30 thenexerts a pressure force onto the pressure element 20 in order to fix thehead 15. The inner member of the fixation element 30 may be screwed intoa threaded bore within the outer member and interacts with the rod 12.It thus becomes possible to fix the rod 12 and the anchoring element 13separately by means of the two members of the fixation element 30.

According to one embodiment pins may be inserted into through holesformed in the receiving part from outside the receiving part such thatthe pins cross the spherical portion being used as a bearing for thehead of the anchoring element and the pins engage with the recessedsurface of the head. Accordingly, the surgeon may fix the degree ofrotation depending on the situation. Without the pins, the anchoringelement can be pivoted in any direction.

In a modification of the application the receiving part 1 can be usedwithout the pins and with an anchoring element having a sphericallyshaped head. Hence, the surgeon can decide depending on the actualsituation at the operation side whether a monoplanar or a polyaxialanchoring device is to be implanted using one and the same type ofreceiving part 1.

It is noted that the seat 7 of the receiving part 1 may also be of aconical or any other shape, wherein the same details of constructionwith regard to the locking device and/or the pins may be applied asdescribed above. Further, the locking device may alternatively beintegrally formed with the inner surface of the second bore.

The pins 33 may be inserted into through holes 34, which are orientedwithin a horizontal plane with regard to the receiving part 1 as shown,e.g., in FIG. 1. However, the invention is not restricted to thatspecific embodiment. An alternate embodiment shown in FIG. 11 indicatesthat the through holes 34 may equivalently be arranged in a longitudinaldirection with respect to the receiving part 1. The pins 33 are theninserted into the through holes 34 from a bottom side of the receivingpart. Other directions of the through holes 34 than horizontal orlongitudinal are possible as well.

A further embodiment is shown in FIG. 12. According to this embodimentonly one through hole 34 is provided to the receiving part 1. The supplyof only one through hole and one pin to be inserted into the throughhole may provide sufficient stability when locking the anchoring element13. In this case, the head 15 of the anchoring element 13 may similarlybe provided with only one flat surface 35 a (FIG. 12 b).

What is claimed is:
 1. A bone anchoring device, comprising: a receivingpart for receiving a rod, the receiving part having a first bore coaxialwith a longitudinal axis, a second bore, and a seat comprising an innerwall; a pin configured to protrude from a hole recessed inside the innerwall of the seat; an anchoring element having a first end configured toattach to a bone and a second end comprising a head configured to bepositioned against the seat to engage the pin when the pin is in thehole, the head comprising a surface having a spherically shaped surfaceportion and an exterior portion from the spherically shaped surfaceportion; wherein the inner wall of the seat is configured to be aroundthe head and to seat the head when the head is positioned in thereceiving part; wherein pivoting of the anchoring element is limited toa single plane by a connection between the head of the anchoring elementand the pin when the head is positioned in the seat and the pin is inthe hole; wherein the connection comprises a guiding surface of theportion recessed from the spherically shaped surface portion of the headthat moves along a guiding surface of the pin resulting in a movement ofthe anchoring element relative to the receiving part being limited tothe single plane; and wherein the pin has a first end and a second endat opposite ends of a longitudinal axis of the pin and wherein the firstend of the pin and the second end of the pin face away from the head ofthe anchoring element when the head is positioned in the seat and thepin is in the hole.
 2. The bone anchoring device according to claim 1,wherein the hole is a through hole arranged such that upon insertion thepin tangentially engages with the portion recessed from the sphericallyshaped surface portion of the head.
 3. The bone anchoring deviceaccording to claim 2, wherein two pins are provided for insertion intorespective through holes formed in the receiving part.
 4. The boneanchoring device according to claim 2, wherein the through hole extendsfrom a first opening formed in an outer surface of the receiving parttowards a second opening formed in the inner wall of the seat, such thatthe pin protrudes out of the second opening in the inner wall of theseat.
 5. The bone anchoring device according to claim 1, wherein the pinis arranged such that the single plane is defined by the longitudinalaxis of the receiving part and an axis of the rod when the rod isreceived in the receiving part.
 6. The bone anchoring device accordingto claim 1, further comprising a pressure element configured to receivethe rod, the pressure element configured to be arranged between the headand a fixation element for transmitting pressure to the head in order tolock an angular position of the anchoring element by means of frictionalforce.
 7. The bone anchoring device according to claim 1, wherein theguiding surface of the portion recessed from the spherically shapedsurface portion of the head is substantially flat.
 8. The bone anchoringdevice according to claim 1, wherein a fixation element is configured tocooperate with the receiving part to lock the anchoring element relativeto the receiving part.
 9. A method of anchoring a bone anchoring deviceto a bone, the method comprising: anchoring a bone anchoring assembly tothe bone, the bone anchoring assembly comprising a receiving part forreceiving a rod and an anchoring element, the receiving part having afirst bore coaxial with a longitudinal axis and a second bore, thereceiving part comprising a through hole; the anchoring element having afirst end for insertion into the bone and a second end positionablewithin the second bore, the second end comprising a surface having aspherically shaped surface portion and a portion recessed from thespherically shaped surface portion; inserting at least one pin in thethrough hole, the pin protruding from an inner surface of the secondbore and moving relative to the portion recessed from the sphericallyshaped surface portion of the second end of the anchoring element toprovide pivoting of the anchoring element relative to the receiving partlimited to a single plane; inserting a rod in the receiving part;adjusting an angular position of the anchoring element relative to thereceiving part around a single axis of rotation; and inserting apressure element in the receiving part, the pressure element configuredto receive the rod; securing the anchoring element relative to thereceiving part with a first fixation element transmitting pressure tothe second end of the anchoring element in order to lock the angularposition of the anchoring element relative to the receiving part bymeans of frictional force; and securing the rod in the pressure elementwith a second fixation element.
 10. A bone anchoring device, comprising:a receiving part for receiving a rod, the receiving part having a firstbore coaxial with a longitudinal axis, a second bore, and a seatcomprising an inner wall; a pin configured to protrude from a holerecessed inside the inner wall of the seat; an anchoring element havinga first end configured to attach to a bone and a second end comprising ahead configured to be positioned against the seat to engage the pin whenthe pin is in the hole, the head comprising a surface having aspherically shaped surface portion and a portion recessed from thespherically shaped surface portion; wherein the inner wall of the seatis configured to be around the head and to seat the head when the headis positioned in the receiving part; wherein the bone anchoring deviceis adjustable between a first position, wherein the anchoring element ispivotable in multiple planes when the head is positioned in the seat andthe pin is not in the hole and a second position, wherein pivoting ofthe anchoring element is limited to a single plane by a connectionbetween the head of the anchoring element and the pin when the head ispositioned in the seat and the pin is in the hole; and wherein theconnection comprises a guiding surface of the portion recessed from thespherically shaped surface portion of the head that moves along aguiding surface of the pin resulting in a movement of the anchoringelement relative to the receiving part being limited to the singleplane.